Cutting die



Feb. 3, 1970 E; o. M ALM I ,903

CUTTING DIE Filed Nov. 20, 1967 Fig 4 United States Patent 3,492,903 CUTTING DIE Eugen Olof Malni, Sandviken, Sweden, assignor to Sandvikens Jernverks Aktiebolag, Sandviken, Sweden, a corporation of Sweden Filed Nov. 20, 1967, Ser. No. 684,106 Claims priority, application Sweden, Nov. 25, 1966, 16,121/ 66 Int. Cl. B26f N46 US. Cl. 83-652 6 Claims ABSTRACT OF THE DISCLOSURE For ensuring that, in forming from an elongated knife a cutting die for use in a clicking cutter, the die is not warped when bent so that the front of the cutting edge diverges from a plane shape, the knife itself is so shaped (in cross-section) that it is thickest in the middle portion thereof and becomes thinner both in the direction toward the cutting edge and in he direction of the back surface or edge. Thus the thckness of the back surface shall be between 0.75 and 0.95 that of the thickest middle portion of the knifes cross-section.

This invention relates to the cutting die art, and is concerned with the avoidance of warping in a cutting die of the clicking cutter type.

The present invention constitutes an improvement of cutting dies in order to avoid that they are warped when they are bent so that the front of the cutting edge diverges from a plane shape. Till now, existing cutting dies with an edge only on one side and with parallel back surfaces have shown a tendency to warp when they are bent so that the edge assumes a concave shape.

According to the invention, this warping tendency is avoided in shaping the cross-section of the back portion of the knife slightly narrowing towards the back side so that the back part of this portion will not be squeezed between the bending tools, which results in that said tendency to warping is eliminated.

The invention will now be described in greater particularity and with reference to the accompanyingdrawing, in which FIG. 1 is a plane view of a bending device conventionally used in forming an elongated knife into a closed figure cutting die;

FIG. 2 is a side view of the bending equipment shown in FIG. 1;

FIG. 3 is a side view of a knife, WhlCll Is not manufactured according to the invention. The figure illustrates the warping which is caused in bending.

FIG. 4 is a cross-section of a modified cutting die according to the invention; and

FIG. 5 is a cross-section of another modification of cutting die, said cross-section embodying the principles of the invention.

The bending equipment which is shown in FIG. 1 comprises a U-shaped jaw 10, with two ridge-shaped contact surfaces 12 and 13, and an opposite jaw 11 with a similar contact surface 14 situated betweenv the contact surface 12 and 13. A knife 15 is placed between the jaws so that the contact surfaces cross the knife and the bending is effectuated by progressively pressing the jaws together by schematically showed loads 16 and 17.

In bending those knives which have a cutting edge only along one side and have a back portion defined by two plane parallel side surfaces there appears a phenomenon which has caused considerable trouble. The contact surfaces of the jaws are pressed into the side surfaces of the knife with such a force that small permanent impressions 3,492,903 Patented Feb. 3, 1970 occur. These are indicated in FIG. 3 and marked 20. The plastic lateral compression which the knife undergoes in this cold working results in that the material strives to dilate in a direction perpendicular to the compression, i.e. in the longitudinal direction of the knife. However, as only the plane parallel side surfaces undergo this cold working and the converging edge portions are clear of the jaws the edge portion will counteract this dilation. The result is that the knife warps so that the edge portion 21 assumes a concave shape which is shown exaggerately in FIG. 3. This makes comprehensive and ditficut works necessary in order to plane the knife after the bending so that the cutting edge will lie along one and the same plane.

In order to avoid this deformation of the die according to the invention the knife is made with a back portion the thickness of which declines towards the back end surface, as shown in FIG. 4. The middle portion 30 of the knife has two plane parallel sides 31 and 32 and at its front portion a converging cutting edge portion 33, comprising two cutting edge surfaces 34 and 35 and a bevel surface 36 on one of the sides, in connection with the side surface 32.

The back portion of the knife 37 is made with a lateral back surface 38 against which a load can be applied when the knife is used in punching. One side of the back portion forms a continuation of the side 31 in the same plane as the latter and the other side 39 of the back portion is somewhat inclined so that the back portion is slightly tapering towards the back end 38. The elevation A of the tapering back portion advantageously can be at least about as large as the elevation B of the cutting edge portion, the bevel surface 36 included. The decrease in thickness C of the back portion should be rather small in order to infringe as little as possible on the back surface 38, for example 0.2-0.4 mm. Usually it is enough to provide the back portion with only a small bevel surface 39, the cutting edge portion thereby being planed in bending to both directions. However, in some cases it may be better to provide a bevel surface 40 also on the op posite side as it is shown with a dashed line in FIG. 4. The back surface should be of a breadth of at least 0.75, and preferably at least 0.80, of the thickness of the knife, and it should mainly be plane or at least blunt enough to provide a good anvil for the punching tool.

In some cases where the bevel surface 36 at the cutting edge is especially high and comprises almost half the elevation of the knife, the side surface 32 will be small and will eventually totally be lacking so that the bevel surfaces 36 and 39 will meet.

The cutting edge portion can have another bevel surface opposite to the bevel surface 36 and situated between the side surfaces 31 and the cutting edge surface 34. FIG. 5 showns a knife which is modified in these last two mentioned respects, so that the sides 36 and 39 will meet at 51 and one bevel surface 50 is situated between the cutting edge surface 34 and the side surface 31. The intersections between the side surface and the bevel surfaces advantageously can be made with a rounding instead of a sharp edge. The surfaces 36 and 50 can, as in the illustrated modification, have different inclinations in order to compensate for tendencies of the knife to bulge when closed figures are to be punched. The surface 50 which is situated on the inner side of the knife then inclines l-5, preferably 24, and the surface 36 on the outer side of the knife inclines 812, preferably 911.

An example of a knife according to the invention is the knife of FIG. 4 of the following dimensions: elevation 19 mm; thickness 2.1 mm.; elevation B of the cutting edge portion 4.65 mm.; elevation A of the back portion 4.65 mm.; elevation of the cutting edge surface 34, 0.6 mm;

and elevation of the cutting edge surface 35, 2.0 mm. measure :0.2 mm. 0

In bending into a cutting die a knife such as the one shown in FIG. 4, one of the bending tools will contact the side 32 but not the converging cutting edge and back portions. On a knife which has a profile as shown in FIG. 5 the bending tool contacts the portion 51. Hereby maximum pressures from the bending tools appear on a portion on the middle of the height of the knife. The above described tendency of the knife to dilate in a longitudinal direction is thus limited to a middle zone along the knife and because of the symmetry there will be no tendency of warping in the front plane of the knife.

Another considerable advantage of the profile according to the invention is that it better keeps straight in rolling, since as Well the cutting edge portion as the back portion are rolled by tilted rolling surfaces which thus keep each other balanced with the result that the tendency of warping laterally is avoided.

I claim:

1. Cutting die comprising a shaped elongated knife having a cutting edge on one edge only and having the opposite edge shaped as a lateral back surface to take up the punching pressure, in which the knife has in crosssection its thickest portion adjacent the middle portion vertically of the knife, and in that the thickness of the cross-section of the knife from said thickest portion diminishes with the distance from said thickest portion as well as in the direction towards the cutting edge as towards the back surface.

2. Cutting die according to claim 1, in which the thickest portion of the knife is of uniform thickness to some extent vertically, and the portion of uniform thickness is situated mainly symmetrically from the middle of the knife vertically.

3. Cutting die according to claim 1, in which the thickest portion of the knife consists of a thickest part and the thickness of the knife decreases in both directions from this part and in that said part is situated about the middle of the vertical dimension of the knife.

4. Cutting die according to claim 1, in which the Width of the back surface is at least 0.75 and at most is 0.95 of the largest thickness of the knife.

5. Cutting die according to claim 4, in which the Width of the back surface is at least 0.80 and at most 0.95 of the largest thickness of the knife.

6. Cutting die according to claim 1, in which the back surface is plane and horizontal.

References Cited UNITED STATES PATENTS 1,049,599 1/1913 Prime 83657 2,191,709' 2/1940 Dedrick 83-652.

FOREIGN I PATENTS 23,410 10/1913 Great Britain.

WILLIAM S. LAWSON, Primary Examiner US. Cl. X.R. 30-346 

